Heat exchanger



May 21, 1968 R. T. MATHEWS HEAT EXCHANGER l1 Sheets-Sheet 1 Filed Feb.5, 1966 INVENT OR RALPH T. MATHEWS Q/W Q .w Emm ATTQRNEY May 21, 1968 vR. 'r. MATHEWS HEAT EXCHANGER Filed Feb. 5. 1966 11 Sheets-Sheet 2INVEN'IOR RALPH T. MAT HEWS ATTORNEY May 21, 1968 Filed Feb. 5, 1966 R.T. MATHEWS HEAT EXCHANGER ll Sheets-Sheet 3 INVEN 1 OR RALPH T. MATHEWSATTORNEY y 1958 T. MATHEWS 3,384,165

HEAT EXCHANGER Filed Feb. 5, 1966 11 Sheets-Sheet 4 FIG.6

INVENTOR RALPH T. MATHEWS ATTORNEY R. T. MATHEWS HEAT EXCHANGER May 21,1968 11 Sheets-Sheet 5 Filed Feb. 5, 1966 INVENT OR PH T. MATHEWSATTORNEY HEAT EXCHANGER Filed Feb. 5, 1966 1,1 Sheets-Sheet 6 FIGSINVENTOR RALPH T. MATHEWS ATTORNEY R. T. MATHEWS HEAT EXCHANGEH May 21,1968 ll Sheets-Sheet 7 Filed Feb. 5, 1966 INVENTOR RALPH T. MATHEWSATTORNEY May 21, 1968 Filed Feb. 3, 1966 R. T. MATHEWS HEAT EXCHANGER llSheets-Sheet 8 FIG IO INVENTOR RALPH T. MATHEWS aw y-Mew ATTORNEY May21, 1968 R. T. MATHEWS HEAT EXCHANGER ll Sheets-Sheet 3 Filed Feb. 5,1966 INVENTOR RALPH T. MATHEWS ATTORNEY R. T. MATHEWS HEAT EXCHANGER llSheets-Sheet 10 Filed Feb. 5, 1966 FIG-15 FIG .19

INVENTOR RALPH T- MATHEWS Q BY Z-?)" FIG. I 7

ATTORNEY May 21, 1968 R. T. MATHEWS HEAT EXCHANGER 11 Sheets-Sheet 11Filed Feb. 5. 1966 INVENTOR RALP H T. MATH EWS ATTORNEY United StatesPatent 3,384,165 HEAT EXCHANGER Ralph T. Mathews, Wallingford, Pa,assignor to E. I. du Pont de Nemours and Company, Wilmington, Del., a

corporation of Delaware Filed Feb. 3, 1966, Ser. No. 524,712 Claims.(Cl. 165-122) ABSTRACT OF THE DISCLOSURE An air type, finned tube heatexchanger having pairs of tube bundles disposed in upright Varrangement, in which the tubes have a length-to-diameter ratio aboveabout 200 and are supported in generally horizontal planes, providedwith means producing air flow generally transverse the tube bundles.

This invention relates to heat exchangers, and particularly to a V-typeheat exchanger utilizing air flow past finned tubes through whichprocess fluid is circulated in order to effect heat exchange.

Heat exchange on a large scale is an exceedingly serious problem for awide range of industries, including, for example, power utilities,chemical manufacture, oil refining, and heating and ventilatinggenerally, the problem being particularly severe in hot regions andthose having water scarcities or water supplies so loaded with salts orthe like as to require expensive pretreatment. However, air type heatexchangers have proved equally useful in cool climates and, in fact,even where there exist plentiful water supplies, because excessiveheating or cooling of natural waters is objectionable from the waterpollution standpoint, and this has led to a growing utilization of airas one component of the heat exchange pair.

A serious disadvantage of conventional air type heat exchangers has beenthe excessive space requirements necessary for their accommodation, plusthe fact that large size air-moving equipment of heavy power consumptionis necessary to maintain the high-magnitude air flows through theapparatus. Moreover, conventional units are not well-suited to theutilization of auxiliary water sprays, which are necessary, ashereinafter detailed, in order to take care of heat loads where theambient temperature of the atmosphere might be temporarily well aboveusual levels, or where process overloads are encountered exceedingsubstantially the dry air design limit of the equipment.

The V-type heat exchanger of this invention cures the foregoingproblems, while affording enhanced efliciency in heat exchange, themanner in which this is accomplished being set forth in the followingdetailed description and the drawings, in which:

FIG. 1 is a somewhat schematic, broken-away perspective view of apreferred embodiment of heat exchanger according to this inventionutilizing three air propulsion units in parallel arrangement to move airpast tube bundles spanning the air paths of all three units,

FIG. 2 is an end elevation view of FIG. 1 taken on line 22 thereof,details of fan assembly support and inlet and outlet connections withthe tube bundles being omitted in order to simplify the showing, but onetype of associated water spray auxiliary being added,

FIG. 3 is a partially broken-away view of a short length of finned tubeemployed in the apparatus of FIGS. 1 and 2,

FIG. 4 is a side elevation view in section showing the moderatetemperature chamber housings for the fans of FIGS. 1 and 2,

FIG. 5 is a sectional side-elevation view detailing the construction andoperative mounting of a preferred design of louvers optionally employedwith the apparatus of FIGS. 1 and 2,

FIG. 6 is a schematic portrayal of a pair of louvers of the type shownin FIG. 5, provided with a balanced force diagram representative of theforces acting on water droplets entrained in the air intake to theexchangers,

FIG. 7 is a plan view of an assembled manifold type tube bundle prior toV mounting in the apparatus of FIGS. 1 and 2,

FIG. 8 is a section taken on line 88, FIG. 7,

FIG. 9A is a fragmentary end view of the tube bundle of FIGS. 7 and 8,

FIG. 9B is a fragmentary cross-sectional end view of a tube bundle suchas that shown in FIG. 9A, except that this bundle is provided with boxheaders,

FIG. 10 is a cross-sectional side elevation of a box header providedwith individual end plug access to individual tubes,

FIG. 11 is a cross-sectional side elevation of an alternate design ofbox header provided with a removable cover plate for access to all tubessimultaneously,

FIG. 12 is a fragmentary transverse cross-section of a tube bundleshowing details of a preferred support strap construction and theassembly with respect to the finned tubes supported thereby,

FIG. 13 is a fragmentary perspective view showing a convenient way ofassembling the tube bundles of this invention,

FIG. 14 is a fragmentary perspective view of an alternate design of tubesupport strap adapted to longitudinal tension assembly within the tubeframework,

FIG. 15 is an end view taken on line 1515, FIG. 14,

FIG. 16 is a side elevation view of a special design of strap employedas a temporary aid in the assembly of finned tubes within bundles,

FIG. 17 is a plan view of a horseshoe type individual tube supportmember shown in assembled relationship with the tube support strap ofFIG. 16,

FIGS. 18 and 19 illustrate a finned tube assembly technique readilyperformed with the aid of the tube support strap of FIG. 16, and

FIG. 20 is a schematic representation of a control system adapted to theautomatic control of heat exchangers according to this invention.

Generally, the heat exchanger of this invention comprises a pair of tubebundles disposed in upright V arrangement, each tube bundle being madeup of a multiplicity of finned tubes having a length-to-diameter ratioabove about 200, the tubes being disposed in generally horizontalsuperposed planes, an inlet header provided with a process fluid supplyline connected in open communication with a first preselected group ofterminal ends of the tubes, an outlet header provided with a processfluid removal line connected in open communication with a secondpreselected group of terminal ends of the tubes, support means carryingsubstantially the full weight of the tubes individually disposedlongitudinally between the inlet header and the outlet headersubstantially transverse rows of the tubes lying in a common horizontalplane within the tube bundles, and powered'means impelling air flowgenerally transverse the tube bundles.

By way of example solely, there is hereinafter described a heatexchanger according to this invention utilized for the cooling of achemical process fluid, because this application presents specialproblems which have not been hitherto solved by apparatus and methods ofthe prior art.

As is well known, the chemical industry usually requires specialmaterials of construction for the fabrication of its vessels, piping andother equipment to minimize corrosion difficulties and, frequently,operations have to be conducted at relatively high pressures andtemperatures, so that heavy stainless steel and, often, even moreexpensive materials are employed, which represents a heavy capitalinvestment. It is thus of the litmost importance that there be extremecompactness in design, with a minimum weight utilization of expensivematerials of construction, not only as regards lengths of connectingpipe lines but also for the tube bundles of heat exchangers and otherapparatus.

Compactness is achieved with the heat exchangers of this invention byutilization of an upright V design for the tube bundles, which resultsin a lateral space saving of approximately 40% over conventionalhorizontal flat bundle exchangers, and by utilizing multiple unitinstallations mounted closely adjacent one another, conveniently atoverhead locations which represent the only above ground space availablein already congested chemical plant manufacturing areas.

Referring to FIGS. 1 and 2, there is shown a typical triple airpropulsion unit design which, collectively, services two tube bundles,indicated generally at and 11, running the full length of the assembly.The apparatus can be conveniently erected on a structural steelframework, indicated generally at 12, on a cubical modular basis, eachof the identical bays A, B and C housing onethird of the apparatus, andeach being provided at the top with a transition fitting 14 within whichis mounted an induction fan 15 drawing the cooling air through the unit.Adjacent units are normally closed off from their neighbors byair-impermeable side walls 16; however, the design of FIG. 1 is specialas hereinafter described, in that the two interior side walls areeliminated on the exteriors of the V arrangement to permit side-directedair flow as shown by the directional arrows.

The heat exchangers are mounted on elevating legs, not shown in FIG. 1but denoted at 17, FIG. 2, presenting the base ends to free air flowfrom the bottom of the construction. Optionally, the base ends areclosed off by adjustable louvers 20, which are advantageous as controlmechanims but which can have a dual function as spray drop collectors,as hereinafter set forth.

FIG. 2 depicts the upright V construction for the tube bundles 10 and11, the included angle of which can vary from about 40 to about 65, withthe 60 angle shown being especially preferred. The cooling air flow inthis instance is, as denoted by the arrows, up from the base of theapparatus, past louvers 20, through the tube bundles in substantiallytransverse flow with respect to the tubes, as shown for the cut-awayportion at the upper end of tube bundle 10, thence out throughtransition fitting 14 under the induced draft of fan 15, with dischargethrough stack opening 22.

Since the cooling air is elevated rapidly in temperature when used dry,as in the usual case, it is essential that the direct drive for fan 15be protected from heat exposure. This is conveniently accomplished (seeFIG. 4) by employing structural steel members (not shown) from whichdepend thermally-insulated ducts 26 which carry air to the fan drivemotor 27 and its direct-connected gear box 28 disposed in verticalorientation within an axially disposed draft tube 29 open at the topend. Thus, fan 15, during rotation, simultaneously draws clean, cool airfrom the outside surroundings radially inward through struts 26 andannularly around motor 27 and gear box 28, thereby affording ventilationat all times during operation. If desired, an externally mountedauxiliary blower (not shown) can be provided outside transition fitting14 to force cooling air through the duct structure to continue coolingeven when motor 27 is shut down for repairs or servicing. However,frequently, natural draft produces enough cooling air circulationthrough struts 26 to keep the motor and gear box cool even when fanoperating ower is. switched oif.

A preferred design of finned tube 33 useful in this invention is thatshown in FIG. 3, this comprising an inner conventional roundcross-section process tube 32, which is fabricated from an appropriatematerial of construction (e.g., stainless steel) resistant to corrosionby the process fluid passed through it and of the necessary strength,heat resistance and other characteristics to accommodate the processfluid from the chemical manufacturing standpoint. The fin assemblyindicated generally at 34 is of unitary construction tightly forced onor otherwise intimately bonded over the full inside periphery coaxiallywith process tube 32, making the construction as nearly integral aspracticable. Aluminum has proved to be a good material of constructionfor fin assembly 34, due to its light weight, ease of working, goodresistance to plant atmosphere corrosion and its high heat conductivity.

As shown, the external fin 34a is a continuous extruded helical screwhaving an outside diameter of, typically, 2.25" with a pitch providingseven to nine fins per inch of tube length for a process tube 32 of 1"outside diameter. The fin tube can typically be approximately 0.040"wall thickness, while individual fins can have a crest thickness of0.018 and a root thickness of 0.065" where water sprays are used.

FIG. 7 is a plan view of a high pressure service manifold type tubebundle, shown in section along line 88 in FIG. 8. The manifold designutilizes, in this instance, four-pass serpentine flow from process fluidinlet header 38, through the finned tubes 33, to process fluid outletheader 39.

As will become clearer from description to follow, tube bundles K10 and11 are built up from parallelly disposed individual finned tube 33sub-assemblies, the straight length ends of which are connected inprocess fluid flow continuation by U-bends 40, welded or otherwisefixedly attached thereto at joints 4'1. Connection is made to headers 38and 39 via enlargements 42 at the tube ends, which are weld-attached inopen communication with the headers, disposed parallel one to anotherbut transverse the tube bundle. Since the finned tube assemblies 3 3 canbe relatively long (e.g., 36 for the three-unit assembly shown in FIG.1), it is imperative that the weight of the tubes be supported atfrequent intervals along their lengths with retention of full freedom toexpand or contract with variation in temperature of the process fluid,particularly when the tubes are full of a liquid phase process fluid, asthis adds appreciably to the gross weight. Otherwise the tube bundleswill sag in random fashion, thereby preventing all uniformity in airflow passage through the bundle as well as any uniform ingress ofcooling liquid sprayed on the outside of the fin assembly 34. Moreover,since individual finned tubes 33 sometimes require that maintenance workbe done on them, tube weight supporting means should preferably bereadily demountable to permit access to any point in the interior of thetube bundle by temporarily displacing adjacent tubes laterally, so as toexpose any particular one for repair without the necessity to firstremove any more tubes from the bundle than is absolutely essential.

Tube support in this invention is provided by demountable support straps46-, shown in plan in FIG. 8 and in side elevation in FIG. 9A, thedetails of which are hereinafter described. First, however, it isbelieved essential to orderly description to treat of the externalframework for the individual tube bundles. This framework is fabricatedfrom conventional structural steel shapes consisting of longitudinalchannels 47 bolt-attached to heavy end transverse I-beams 48. To providelateral stiffening at intervals along the length of the bundle,additional, somewhat lighter transverse I-beams 49 have beenincorporated, these being provided with fixedly-attached end plates 49afor bolt attachment to the webs of channels 47. Channels 50, whichconstitute the support members receiving the ends of support straps 46,are fixedly attached to the inwardly disposed lengths of I-beams 49.

The weight of headers 38 and 39 is carried in yoke plates 51 mountedwith yoke openings 51a disposed parallel to but outboard of longitudinalchannels 47, plates 51 being welded or otherwise joined to the webs ofchannels 47.

Referring to FIGS. 1 and 9B, the right-hand end of the tube bundle isthe top end of the bundle in the upright V final assembled position.Stiffening plates 54 are weldattached across the channel 47 flanges atappropriate intervals to stiffen and strengthen the construction,whereas triangular-shaped pieces 55 securely welded or otherwiseattached to the web at the ends of channels 47 constitute the cornerattachment points to the upper ends of the upright frame pieces definingbays A, B and C of FIG. 1, whereas pad pieces 56 constitute basesupports for the framework denoted generally at 57 to which transitionfittings 14 are attached.

Tube bundles 10 and -11 are supported in upright V arrangement uponlongitudinal pedestal strip 23 (FIG. 2), the central portion of which isclosed off for its full length to bar by-pass air flow. It is mostconvenient, as hereinafter described, to assemble all of the tubeswithin framework 12 while the latter is laid flat and thereafter liftthe fully assembled tube bundle pairs into place on opposite sides ofpedestal strip 23. Since the tube bundles are relatively heavy, thisfinal assembling is most readily accomplished with the aid of a powercrane and it is preferred to provide drilled holes, such as hole 24 intriangular pieces 55 (FIG. 912) for ready insertion of the crane lifthook.

In the interests of weight saving, channels 50 are preferably aluminum,although they can equally well be aluminized steel to reduce possibleelectrolytic interaction with aluminum support straps 46. Where aluminumchannels 50 are employed, they are preferably isolated from directcontact with l-beams 49 by interposition therebetween of a micartastrip, not shown.

Channels 50 are assembled with their webs inwardly disposed from theinner flanges of transverse I-beams 49, thereby forming oppose-denclosed box constructions 59 adapted to receive the opposite ends ofsupport straps 46 through slots 6% spaced at regular intervals along thechannel length.

There exist a number of ways in which channels 50 can be attached toI-beams 49, so as to form a unit construction therewith, one of which(FIG. 13) constitutes the use of angle clips 61 adapted to be attachedin opposition to the two sides of the I-bearns by a common through-bolt62 with lower legs wedged tightly beneath the adjacent flanges of theI-beams, micarta isolation strips (not shown) being again used toisolate aluminum components from steel.

As seen particularly in FIGS. 9A, 9B, 12 and 13, support straps 46 arestiff but springy pieces (typically 2" x 12% x thick aluminum) havingtheir central lengths bent in a regular repetitive undulatory pattern toform individual concave recesses formed on a circular arc conformingquite closely to approximately 60 of the lowermost peripheral expanse offinned tubes 33. The rigorous development of a preferred design of strap46 is shown schematically in.FIG. 12. Here the longitudinal center linesof the strap ends are drawn in in broken line representation and aconstruction line drawn from the center line at the left-hand side,where the strap is first bent arcuately, to the center line at theright-hand side, where the straight strap end recurs again. Thisconstruction line makes angles of 150 measured counterclockwise as seenin FIG. 12 with respect to both left-hand and right-hand strap endcenter lines. The pitch of the undulations is such that neighboringfinned tubes 33 in any given row are spaced one from another on equalpitches of, typically, 2 /2 for the specific tubes of 2% outsidediameter hereinbefore mentioned, thus leaving a longitudinal A airpassage clearance between adjacent tubes of any given horizontal row. Asmall clearance of typically is provided between the tops of the finnedtubes 33 and the undersides of the support straps for the nextsucceeding row thereabove, which accommodates some lack of straightnessin adjacent tubes, however, tubes 33 are brought up snugly into fixedspotted relationship one with another by the springiness of individualtubes, locking the tubes in a tight uniform tube center-to-tube centerequilateral triangular pattern g, FIG. 12, throughout. At the same time,essentially the full weight of each row of the tubes is carriedexclusively by the support straps 46 and transmitted in turn to channels50, I-beams 49 and the bundle framework generally. Thus, there is nosagging of the finned tubes, provided that support straps 46 areemployed at relatively short spacings (e.g., every four feet) ofunsupported tube length extending between the extreme ends of the tubebundle.

The support strap hereinabove described is the subject of my patentapplication Ser. No. 524,811 of common assignment filed of even dateherewith.

The convenience in assembly of the foregoing construction is portrayedin FIG. 13, which illustrates how successive tube layers can be readilybuilt up in sequence between pairs of adjacent support straps 46.

It is usually preferred to assemble the tubes in a bundle by bringingthem into place from the top, and this is most easily done by laying thebundle framework flat before attachment thereto of the uppermost I-beam49, channel 50 sub-assembly, denoted generally at F in FIG. 13. Thelower ends of straps 46 are then inserted in order from right to left inslots of the bottom channel 50' successive finned tubes 33 being nextplaced one above the other in each row, cradled within the opposedundulations of adjacent straps, after which the next rows in horizontalprogression to the left are built up in turn. As shown in FIG. 13, theextreme right-hand strap denoted 46 is actually only a half-strap,retained at its end abut ting channel 47 by a welded clip 67, thepurpose being to utilize to the utmost all available cross-sectionalarea within the bundle framework for the accommodation of heat exchangetubes. Any unused open area remaining is closed off by spring-clippedpanels 68 (FIG. 9A), which thus prevents by-pass of air through theunit.

Usually, the weights of tubes 33 bias straps 46 right- Ward'ly as seenin FIG. 13, so that there is automatic alignment of the straps in theirproper final positions; however, if desired, a rake tooth retainer (notshown) can be used to temporarily secure the straps against lateraldisplacement one from another.

An exceptionally convenient temporary retainer is that detailed in FIG.13, straps 46 being in this instance provided with slots 66 at theirupper ends deep enough for full reception of tension bar 69, which isadvanced in notch-by-notch progression from right to left. The lefthandend of bar 69 is formed into a hook 70 adapted to overlie the bottom ofslot 66 in the left-most strap 46 and thereby lock all tube rows to theright against any shifting during the time that the tube bundle is beingassembled.

The top edge of tension bar 69 is provided with a succession of equallyspaced notches 71 located distances apart equal to the final desiredspacing of individual straps 46 one from another. A slot 72 large enoughto slidably receive tension bar 69 is cut in longitudinal channel 47 atthe points where support straps 46 are employed, and there is slippedover the right-hand free end of the bar a freely slidable slotted keeperpiece 73 which drops by force of gravity into successive notches 71 onbar 69 during its advance to the left, securely locking all straps inplace until another notch advance is desired. When all finned tubes 33have been assembled within the bundle, sub-assembly F can be loweredinto place to an extent where the upper ends of straps 46 just enter topslots 60, which position can be preserved by using temporary lockingdowels inserted through holes 75 drilled in the web of channel 47. Thentension bar 69 can be rocked slightly to disengage book 70 and the barwithdrawn completely through slot 72, after which the sub-assembly F islowered to final position with upper ends of straps 46 fully insertedwithin slots 60. Finally, sub-assembly F is bolted securely at both endsto the longitudinal channels 47 and the tube bundle assembly iscomplete.

An alternate, somewhat simplified design for retention of support straps46 is detailed in FIGS. 14 and 15, this having the advantage that straps46 can be assembled under predetermined longitudinal tensions, which canbe particularly desirable in installations where there existsconsiderable transmitted vibrational stress from adjacent plantequipment, such as reciprocatory compressors or the like. In this case,an exceptionally tight tube assembly is desirable to insure thatinvariant air passages are maintained throughout the tube bundles.

The alternate design dispenses with channels 50 and substitutes I-beams49 which are slotted on the inboard flanges at 78 to receive the ends ofthe straps, again provided with longtiudinal slots 66, which thenoverlie the web portions 49' of the I-beams. The outer edges of theslotted ends of the straps are cut away to form notches 79 which receiveoppositely disposed C-profile spring clamps 80, brought into tightabutment at the top edges against the underside of the inboard flangesof I-beams 49 and at the bottom edges against the lower ends of notches79 by tightening the nuts 81 on bolts 82 threaded at both ends andpassed through drilled holes in web 49'. It will be understood that anidentical construction is employed on the other ends of straps 46,making it possible to effect tension adjustment at will from either sideof the tube bundles.

Regardless of which design is employed, straps 46 apparently cross bracefinned tubes 33 in tight rigidity, which enables tilting of theassembled tube bundles into any plane without change of tube position.

It is sometimes desirable, as an aid in the assembly, to supportindividual tubes in temporary position at preselected points fartherapart than the 4 span intervals hereinbefore described, and theapparatus shown in FIGS. 17-19 has been devised for this purpose. Here astrap 46" identical in all respects with straps 46 hereinbeforedescribed, except with the modifications now to be detailed, is employedsolely for assembly purposes.

Strap 46" is notched along both edges as indicated at 85 in the rootportions of the undulations so as to receive U-piece-s 86, which areproportioned to just abut the crests of the opposed undulations on thestrap 46 disposed to the right, thereby affording a temporary base forsupport of the finned tube 33 thereabove. It is contemplated that straps46" and their U-pieces 86 will be employed at alternate intervals of,for example, every 8' apart over the tube bundle length, therebyaffording support and location to individual tubes while they are beingrolled in or otherwise attached to their headers. Thereafter, when thefinal straps 45 are put into place, these are first assembled in thealternate vacant positions existing between straps 46". Then the latterare pulled and replaced by regular straps 46, bringing the assembly tocompletion.

For purposes of the description, a tension bar as is shown in FIG. 18 inconjunction with notched end straps 46 and 46".

While, as hereinbefore mentioned, louvers 20 are optional, their use isespecially advantageous where critical heat exchange control is to bemaintained, or where water sprays are employed as cooling aids; however,louvers possess advantages even in dry air operation, and where manualcontrol is relied upon, so that their general use is preferred.

Referring to FIGS. 2, and 6, the louvers are mounted within a squat,square cross-section breeching 88 located beneath the upright V tubebundle assembly and athwart the lowermost air passage of the unit, whichis provided with a multiplicity of longitudinal members 87, upon whichare pivotally mounted the co-parallel individual louvers 20. Theselouvers are typically approximately 8 long, measured tip-to -tip, andare spaced at uniform distances apart of about 4", so that they overlapwhen closed, as will be apparent from the right-hand broken-linerepresentation of one louver shown in closed position.

It will be noted that the left-hand louver 20' is of shortenedconstruction, so that it presents no interference troubles in the courseof closure.

Louvers 20 are formed with reverse curvatures as regards the bladeportions 20a and blade portions 2%, both being formed, typically, on 5"radii. Blade portions 20b are provided with oppositely disposed Ucross-section water collection gutters 89 and 99, respectively, eachserving an individual side of a louver 20 on which it is mounted. It iscontemplated that louvers 20 will be mounted at a slight slope inwardlytoward the center of the unit, so as to obtain ready gravitationaldrainage of water collected thereon into a central sump 91 (FIG. 2) fromwhich it can be recycled as spray water by centrifugal pump 92, wheresprays are used as hereinafter described, or run to waste if the wateris wash water or otherwise contaminated.

Louvers 20 are operated in unison through bar connector 93, which isprovided with upstanding finger portions 94 fixedly attached to the endsof all blade portions 2%, and actuating crank 95 pinned to bar connector93 at the right-hand end of the sub-assembly. In order to coordinate theactuation of the abbreviated righthand louver with its neighbors, thereis provided a short connector bar 96 securely attached through fingerportions 97 to the tip ends of the two rightmost louvers shown in FIG.5.

The foregoing design of louver was evolved in order to entrap andconserve virtually all droplet water draining from the tube bundles intheir upright V mounting, since the resultant of forces (gravitationaland air supply velocity) acting on water drops, as shown schematicallyin FIG. 6, is a component of force x directed against louvers 20 for thefull range of settings of the louvers. Accordingly, the water dropletsimpinge on the louvers and drain via gutters 89 and 90 into sump 91.This is an important function of the louvers which, besides theirstreamlined direction of cooling air over the entire crosssection of theapparatus, are simultaneously adapted to collect and retrieve anycooling water, or cleansing water used to wash down finned tubes 33 fromtime to time.

A preferred auxiliary water spray arrangement is depicted in FIG. 2 andcomprises manifolded spray nozzles 190 mounted, typically, in multiplesof four across the width of a tube bundle 72" wide, the nozzles orientedwith openings generally parallel to the outboard faces of the tubebundles at spacings therefrom of about 12''. Typically, the nozzles candischarge 1-10 gals/hr., depending upon the heat removal requirements ofthe particular installation. As will be clear from description tofollow, both the location and the spacing of the sprays longitudinallyof the bundles can be varied widely to obtain predetermined coolingpatterns. Spray water is supplied to nozzles 100 by one or more pumps 92via supply lines 101 and 102, with gravitational drainage returneffected via collection gutters 103 and drain pipes 104 discharging intosump 91.

Nozzles 100 can be of either the atomizing type or can be relativelycoarse sprays, the latter being ordinarily preferred for exteriorlymounted nozzles because the fins of tubes 33 are then well-wetted, whichproduces the maximum cooling action. Water atomized into the air streamlowers the air temperature, thus reducing the mean temperaturediiference (abbreviated MTD in the literature) between the cooling airand the process fluid in transit through finned tubes 33 without,however, extensively wetting the tubes. Atomized water spraying issometimes advantageous to reduce the temperature of the ejected air atthe hot side (inboard faces) of the tube bundles and thus is preferablyapplied by sprays which are disposed interiorly of the tube bundles, asby omitting one row of finned tubes 33 of a given bundle and directingthe spray atomizers in opposition, or at right angles, to the air flowthrough the bundles.

I have found that intermittent spraying of finned tubes 33 isparticularly efficient in the utilization of cooling water, this typespraying being effected by reciprocallymounted nozzle assemblies (notshown) adapted to traverse the tube bundles longitudinally, with returntimed to occur prior to drying of water on the tube fins, therebyminimizing the build up of heat-insulating deposits on the fins.

It is essential that clean water be employed as the spray liquid, andthe use of filters, sedimentation removal of solids within sump 91 andeven treatment of the water with wetting agents and/or soluble corrosioninhibitors are all worthwhile procedures. Moreover, the water should beof low sedimentation characteristics on drying.

The upright V tube bundle arrangement according to this invention hasproved exceptionally advantageous when auxiliary spray water isutilized, it being found that the enetration of water droplets fromnozzles 100 occurs to an appreciable extent throughout practically theentire transverse extent of the air path of a 4-6 tube bank size heatexchanger.

A problem with horizontally disposed prior art heat exchangers has beenthat spray water collected between tubes unpredictably until such severeflooding occurred that random extensive areas would actually dump largeamounts of water at different times impossible to anticipate. Thecooling water was thus wastefully employed and oftentimes did as muchharm as good, since it blocked air flow past the heat exchange tubesover relatively large areas and, in addition, unbalanced the air passageso that some areas of the exchanger preferentially funneled air throughat exceedingly high velocities whereas, in others, there existedsubstantially zero flow.

In comparison, the V tube bundle arrangement preserves an exceedinglyeven stratified air flow throughout the entire construction, as has beenverified by smoke tests, especially when side walls 16 are employed,with or without louvers 20. Moreover, there is no localized waterflooding of the tubes, any excess fin-wetting water draining downwardlyfrom one tube layer to its next-lower neighbors and thence into gutters103 with speedy return to sump 91 via drains 104. This latter is animportant advantage, not only from the standpoint of conserving highcost spraying water but also because it eliminates spray drift, which isa nuisance to plant personnel and a potential hazard to electrical andother process equipment located anywhere in the vicinity.

Referring to FIG. 1, the usual operation of heat exchange unitsaccording to this invention is that represented by the discharge airflow directional arrows drawn for the two outside units. That is, withlouvers 20 opened at the bottom, air is impelled through the units,generally transversely inwardly past the tubes of the bundle pairs in Varrangement, and thence past the blades of induction fans 15, withdischarge of the heated air through stacks 22.

The typical V heat exchanger design hereinbefore detailed dimensionallyby way of example, which allows for A" clearance between adjacent finperipheries, has proved to be especially effective in maintainingconstant air velocities through the units. Thus, with air supplied,through louvers 20 at a velocity of approximately 1200'/ min. there is,of course, throttling in passage past the tubes of bundles and 11, whichaccelerates the air flow. However, since the discharge from both bundlesis thereafter combined inside the V, the final discharge velocitymaintained is again at about the original 1200/ min. supply level.

I have found that, throughout practically the entire extent of theUnited States, one can rely on dry air cooling without any auxiliarywater spray utilization for at least of the time for most chemical plantcooling processes. However, it is highly desirable to make provision forat least limited water spray cooling sup lementation in locations whereexceedingly high dry bulb temperatures are encountered over protractedperiods of time. In addition, spray supplementation should, of course,be provided where an adjustable range of process fluid cooling isnecessary incident to the manufacturing operation for which the heatexchange is being conducted. Finally, spray supplementation has adistinct economic advantage in many instances, because the air volumesto be handled are sharply reduced when Water sprays are available ascooling aids, reducing fan power costs and permitting certain fans to beshut off entirely in order to effect repairs or general maintenance.

The heat removal advantage of spray supplementation is so marked in mostinstances that a 300-400% increase in heat removal capability on the airside is often very quickly obtained after water spraying of the tinnedtubes 33 is commenced. The reason for this is evidently that maintenanceof a water film on fins 34a and their support tubing increases greatlyevaporation of water from the fins and the temperature differentialbetween the hot fluid passing through tubes 32 and the fins. Soetfective is this action, that I have found that I can easily obtaincondensation of process fluids with my exchangers, and even a measure ofappreciable process liquid sub-cooling, all as taught with reference toFIG. 20.

Atomizing sprays as hereinbefore described are generally less effective;however, they do increase the mean temperature difference by loweringthe air temperature appreciably by the heat take-up ascribable tocooling water evaporation and are definitely worthwhile, either alone orin conjunction with coarse s rays.

Extensive operating experience has shown that V-type heat exchangersaccording to this invention are usually superior to conventional riverwater-cooled shell-andtube exchangers, and, in many cases, are alsobetter than expensive cooling tower water-cooled installations.

FIGS. 10 and 11 show typical box header constructions which can beutilized for low pressure installations, FIG. 10 detailing a headerhaving multiple plugs 35 in longitudinal alignment with finned tubes 33,so as to permit ready rod or hose cleaning. FIG. 11 shows a headerclosed by a common plate 36, provided with a gasket 37, preventingleakage.

Obviously, as is well known in the .art, a wide variety of process fluidflow patterns through preselected groups of tubes within the heatexchangers can be readily obtained by sub-dividing the box headers withtransverse flow-routing partitions, and this is accordingly not furtherelaborated. Also, if desired, the process liquid can be cooled bydividing it into parallel flow through tube bundles 10 and 11separately, or by routing it in series through first one bundle and thenthe other, or in various combination series-parallel flows best-suitedto the requirements of the particular installation, the design affordinga broad choice of alternatives in this regard.

Turning now to FIG. 20, there is shown in schematic cross-section aV-type heat exchanger according to this invention provided withautomatic control facilities.

In this instance, the hot vaporous process fluid is introduced via line109, which is divided into separate branches 109a and 10% leading to theinboard tubes of tube bundles 10 and 11, respectively. A box headerconstruction, as shown in cross-section in FIG. 10, routes the flow intothe plane of the figure for the first vaporous fluid pass, as indicatedby the arrow representation within sections 10a and 11a, FIG. 20,whereas reverse flow as a second condensed liquid pass occurs insections 10b and 11b. This produces a hot condensate product withdrawnfrom lines 110a and 110b, which latter are manifolded into line 111.

A portion of the condensate, determined by the liquid level maintainedat the bottom of sections 10b and 11b, which are cross-tied byconnections 110a and 11%, is retained in the sub-cooler sectionsconsisting of first passes 10c, 11c and second passes 10d, 11d, the coldcondensate discharged therefrom leaving via lines 115 and 116,respectively.

Hot condensate discharge line 111 is provided with a conventionalair-operated flow control valve 117, and cold condensate discharge line112 is provided with a similar automatic valve 118. These two flowcontrol valves are connected in reverse-acting relationship, so that oneopens when the other closes responsive to a signal transmitted to bothvalves via control line 119 running from conventional temperaturecontroller 120. Temperature controller 120 operates on the basis of thetemperature of the commingled hot and cold condensate mixture, sensedvia line 123 at a point far enough removed downstream from the junctionof lines 111 and 112 to insure that intimate mixture has been obtained.

Control of sub-cooler operation is achieved by interposing a set ofautomatically operated louvers 124 athwart the exit air passage from thesub-coolers 10c, 10d and 11c, 11d, these louvers being operatedcollectively as hereinbefore described with respect to FIG. by an airpressure actuation mechanism 125 responsive to a control signaltransmitted from temperature controller 120 via line 126. In operation,it is usually satisfactory to confine the condensate flow controleffected by valves 117 and 118 to the 310 lbs. part of the conventional3-15 lbs. instrument air pressure range, reserving pressures above lbs.to effect progressive throttling closure of louvers 124, which otherwiseremain full open.

Condensate is withdrawn from the system via line 128, into which lines111 and 112 discharge, provided with air pressure-actuated flow controlvalve 129. This valve is responsive to a signal transmitted via line 130from level controller 131 connected in parallel across the high and lowlevel points of the first pass of the sub-cooler, denoted 10c.

It is usual, in chemical manufacturing practice, to maintain a quiteconstant pressure in the vapor input line 109, and conventional pressurecontroller 134 is provided to effect this, the ambient vapor pressurebeing sensed vi-a line 135 and control signals then generated which arepassed via line 136 to control the pitch of variable pitch fan 15, or,via line 137, to conventional actuator 138 adjusting the position oflouvers 20.

The supplementation water sprays are not detailed in FIG. 20, in orderto simplify the showing, however, it will be understood that anarrangement such as that shown in FIG. 2 is suitable. This comprises asump 91 with float-controlled fresh water make-up replenishment andwater delivery throttling valve 140 interposed in line 101 running viafilter 132., to the spray nozzles 100 (not shown in FIG. 20). Both thedrive motor 141 for pump 92 and throttling valve 140 are controlled viasignal line 142 provided with a thermal switch 143 disposed in the heatexchanger air intake passage. Thus, when the intake air attains atemperature too high for effective cooling, thermal switch 143 closesthe power circuit to drive motor 141 and simultaneously opens valve 140a suitable amount to commence supplementary water spraying. As theambient air temperature increases, valve 140 opens wider, thus supplyingadditional spray water to meet the heat removal requirements.

I have found that the greatest economies in heat exchanger constructionare obtained by employing relatively long finned tu'be assemblies 33(e.g., of length-to-diameter ratios above about 200) and these arereadily obtainable from the fabricators; however, there has hithertobeen no method of assembling and supporting the long, naturally sagginglengths. Support straps 46 are effective for tubes of any conceivablelength and, thus, tube length constitutes no limitation in theutilization of my invention.

Most often, air type heat exchangers are mounted at high, quiteinaccessible locations, such as at rooftop levels, for example, so thatthey are subjected to gusting winds and full exposure to the weather.Side walls 16 are then especially important to the maintenance ofuniform air flows. Additionally, arcuately recessed plates 30 slipped inpiace over finned tubes 33 in prolongation of sidewalls 16 restrict airby-passing at the tube bundle ends.

Very satisfactory protection from rain water intrusion is obtained byproviding stacks 22 with internal peripherally arranged collectiongutters disposed just below the fan level, fans 15 quite effectivelythrowing the rain water outwardly by centrifugal action, whereupon it isdrained off through a conventional storm water drainage system notdetailed.

Also, it is sometimes helpful to vary the air throughput of selectedheat exchange units in order to safeguard against freezing the processliquid being cooled. One example is the specific apparatus detailed inFIG. 1. Here provision is made for optional reverse air flow during coldweather through the middle heat exchange unit, housed in bay B, withdischarge laterally through the cut away side walls 16 into the adjacentheat exchange units housed in bays A and C. This is readily accomplishedby closing the louvers 20 on the bottom of bay B, and reversing thedirection of fan 15 operation for the center unit. Under thesecircumstances, air is drawn in from the top of the center unit,contacting the hottest process fluid first in its reverse transitthrough the tube bundles, after which this heated air is dischargedlaterally into the air intakes of the adjacent units in bays A and C asindicated by the air flow directional arrows. This tempers the airintakes to the latter, and reduces the overall heat removal for thethree-unit combination assembly to a level accommodating severe coldweather conditions. It will be understood that, in warm weather, thecenter unit is operated with louvers 20 open and the fan draw ing airinwardly, the same as its two neighboring units, the absence of the sidepartitions causing little or no difficulty.

A great variety of control facilities are available to the designer inthe case of air type heat exchangers, especially convenient devicesbeing variable pitch fans 15. Also, while the foregoing description hasbeen directed to induction fans, solely by way of example, thesubstitution of propulsion blowers located at the intake ends of theunits is, of course, entirely practicable; however, the induction fandesign has the advantage that its housed protection as shown in FIG. 4shields motors and gear boxes from water spray damage to perhaps thefullest extent.

Also, while the most extensive present use of the construction is forprocess fluid cooling, the units are equally well-adapted to heatingservice, if this is desired. Employment of the term fluid as descriptiveof the material flowing through finned tubes 33 is intended to becomprehensive of both vapors and liquids and, while substantiallyhorizontally disposed tubes 33 have been hereinbefore specificallytaught, support straps 46 can be fabricated in slightly twistededge-to-edge slopes, so as to furnish a slight progressive downwardinclination throughout successive rows of tubes insuring gravitationalliquid flow therethrough, if this is desirable. Accordingly, the termgenerally horizontal, as used in the claims, is intended to comprehendalso tubes slanted enough to be self-draining.

It is convenient to provide walkways between neighboring batteries ofheat exchangers constructed according to this invention, and this hasproved completely practicable for the very light maintenance work whichthe units require. The only regular maintenance required is lubricationsupply to the individual fan gear boxes 28, and this is readily achievedby using externally located oil supply-dip stick assemblies cut-in inparallel circuit with the counterparts integral with the conventionalapparatus components.

A very important advantage of the construction is that support straps 46are sufiiciently springy so that, when disengaged from slots 60 at oneend, they can be deflected laterally a sufiicient amount to permitremoval of a defective tube from anywhere within the tube bundles withthe prior disengagement of only a few overlying tubes being necessary toopen the way. This is made possible by the relatively shallow cradleportions of the straps abutting the finned tube peripheries, whichreadily free the tubes from restraint when straps 46 are temporarilybent aside.

From the foregoing it will be apparent that this invention can bemodified in numerous respects without departure from its essentialspirit, and it is accordingly intended to be limited only within thescope of the following claims.

What is claimed is:

1. A heat exchanger comprising, in combination:

(a) a pair of tube bundles disposed in upright V arrangement within astructure provided with air throughput passages at upper and lower endsbut closed off from the exterior by substantially air-impermeable sidewalls,

(b) each tube bundle being made up of a multiplicity of finned tubeshaving a length-to-diameter ratio above about 200, said tubes beingdisposed on substantially triangular centers in generally horizontalsuperposed planes,

(c) an inlet header provided with a process fluid supply -line connectedin open communication with a first preselected group of terminal ends ofsaid tubes,

(d) an outlet header provided with a process fluid removal lineconnected in open communication with a second preselected group ofterminal ends of said tubes,

(e) support means carrying substantially the full weight of said tubesindividually disposed longitudinally between said inlet header and saidoutlet headcr generally transverse rows of said tubes lying in a commonsubstantially horizontal plane within said tube bundles oriented in saidV arrangement, and

(f) powered means impelling air flow generally transverse said tubebundles.

2. A heat exchanger according to claim 1 wherein said tube bundles areprovided at preselected intervals with partitions extending across thefull widths of said bundles interiorly of said V arrangement and saidpowered means impelling air flow generally transverse said tube bundlesare disposed in parallel relationship one with another longitudinally ofsaid tube bundles and on opposite sides of said partitions.

3. A heat exchanger according to claim 1 provided with adjustablelouvers disposed in line with the air throughput course of said heatexchanger.

4. A heat exchanger according to claim 3 provided additionally withautomatic control means adjusting the degree of opening of said louversresponsive to a sensed temperature which is a function of the currentheat-exchanging capability of said heat exchanger.

5. A heat exchanger according to claim 1 provided with water spraysdischarging water into said air flow genera-11y transverse said tubebundles.

References Cited UNITED STATES PATENTS 2,650,802 9/1953 Huet 165-1762,680,603 6/1954 Taylor 261 3,148,516 9/1964 Kals 261-140 FOREIGNPATENTS 900,407 7/1962 Great Britain. 904,959 9/ 1962 Great Britain.

ROBERT A. OLEARY, Primary Examiner.

T. W. STRUELE, Assistant Examiner.

